1. Field of the Disclosure
This disclosure relates generally to oilfield downhole tools and more particularly to modular drilling assemblies utilized for drilling wellbores having one or more enlarged diameter sections.
2. Description of the Related Art
To obtain hydrocarbons such as oil and gas, boreholes or wellbores are drilled by rotating a drill bit attached to the bottom of a drilling assembly (also referred to herein as a “Bottom Hole Assembly” or (“BHA”). The drilling assembly is attached to the bottom of a tubing or tubular string, which is usually either a jointed rigid pipe (or “drill pipe”) or a relatively flexible, spoolable tubing commonly referred to in the art as “coiled tubing.” The string comprising the tubing and the drilling assembly is usually referred to as the “drill string.” When jointed pipe is utilized as the tubing, the drill bit is rotated by rotating the jointed pipe from the surface and/or by a motor contained in the drilling assembly. In the case of a coiled tubing, the drill bit is rotated by the motor. During drilling, a drilling fluid (also referred to as “mud”) is supplied under pressure into the tubing. The drilling fluid passes through the drilling assembly and then discharges at the drill bit bottom. The drilling fluid provides lubrication to the drill bit and carries to the surface rock pieces disintegrated by the drill bit in drilling the wellbore via an annulus between the drill string and the wellbore wall. The motor, if used, may be rotated by the drilling fluid passing through the drilling assembly, by an electric motor, or other suitable driver. A drive shaft connected to the motor and the drill bit rotates the drill bit.
In certain instances, it may be desired to form a wellbore having a diameter larger than that formed by the drill bit. For instance, in some applications, constraints on wellbore geometry during drilling may result in a relatively small annular space in which cement may flow, reside and harden. In such instances, the annular space may need to be increased to suitably fix a casing or liner in the wellbore. In other instances, an unstable formation such as shale or salt may swell to reduce the diameter of the drilled wellbore and make it difficult to install a liner or casing. To compensate for this swelling, the wellbore may have to be drilled to a larger diameter while drilling through the unstable formation. In still other situations, such as in monobore drilling, it may be desired to increase a diameter of the wellbore to accept casing that is to be expanded. Furthermore, it may be desired to increase the diameter of only certain sections of a wellbore in real-time and in a single trip.
The present disclosure addresses the need for systems, devices and methods for selectively increasing the diameter of a drilled wellbore.